Semiconductor diode lasers were developed in 1962 almost simultaneously by several groups of workers. Since then much development work has evolved in the development and use of light emitting semiconductor diodes.
There are at least three groups of diode lasers and are classified according to structure. Simple diode lasers are called homostructure lasers because they are made of a single semiconductor material. A homostructure diode laser would comprise, for example, n-type and p-type gallium arsenide (GaAs). The recombination of electrons injected from the n-region into the p-region with holes extending in the p-region causes the emission of laser light.
In a single-heterostructure semiconductor laser device an additional layer of aluminum gallium arsenide (AlGaAs), for example, is added. This type of crystal has had some of the gallium atoms in the gallium arsenide crystal replaced by aluminum atoms. The injected electrons are stopped at the aluminum gallium arsenide layer (junction) resulting in a higher degree of concentration of light emitted.
In a double-heterostructure semiconductor laser device, for example, three layers of gallium arsenide are separated by two layers of aluminum gallium arsenide. The barrier set up by the preselection of n-type or p-type materials causes even further confinement of the light emitted.
According to the present invention, several embodiments or semiconductor laser devices, are disclosed. One embodiment discloses a homostructure optical device with symmetric optically excited regions. There are two controlled regions, one on either side of the light emitting junction.
Another embodiment of the present invention discloses a single-heterostructure optical device with a single optically excited region. With the biases set forth as described, a small input light signal or small current change produces large changes in the output of the diode.
Another embodiment of the present invention discloses a double-heterostructure optical device with dual optically excited regions. In this embodiment there are two areas on the device which may trigger the laser output light in response to either one or the other of optical light input.
A further embodiment of the invention disclosed herein integrates an electronic device with a diode laser in accordance with the principles of the present invention. Small optical or electronic signals produce large changes in laser current and thus a large change in output light.
Still even a further embodiment of the present invention discloses an optical triode laser device in which a small input light results in an amplified light output signal. On a single semiconductor laser diode crystal, a field effect transistor together with an optically controlled gate is used to modulate the current to a short section of a semiconductor laser.